linux-hardening - [PATCH 51/64] tracing: Use struct_group() to zero struct trace

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Date:   Tue, 27 Jul 2021 13:58:42 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH 51/64] tracing: Use struct_group() to zero struct trace_iterator

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark region of struct trace_iterator that should
be initialized to zero.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/trace_events.h | 26 ++++++++++++++------------
 kernel/trace/trace.c         |  4 +---
 2 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index ad413b382a3c..cadad77fe524 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -101,18 +101,20 @@ struct trace_iterator {
 	bool			snapshot;
 
 	/* The below is zeroed out in pipe_read */
-	struct trace_seq	seq;
-	struct trace_entry	*ent;
-	unsigned long		lost_events;
-	int			leftover;
-	int			ent_size;
-	int			cpu;
-	u64			ts;
-
-	loff_t			pos;
-	long			idx;
-
-	/* All new field here will be zeroed out in pipe_read */
+	struct_group(init,
+		struct trace_seq	seq;
+		struct trace_entry	*ent;
+		unsigned long		lost_events;
+		int			leftover;
+		int			ent_size;
+		int			cpu;
+		u64			ts;
+
+		loff_t			pos;
+		long			idx;
+
+		/* All new field here will be zeroed out in pipe_read */
+	);
 };
 
 enum trace_iter_flags {
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c59dd35a6da5..9f83864b0be6 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6691,9 +6691,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		cnt = PAGE_SIZE - 1;
 
 	/* reset all but tr, trace, and overruns */
-	memset(&iter->seq, 0,
-	       sizeof(struct trace_iterator) -
-	       offsetof(struct trace_iterator, seq));
+	memset(&iter->init, 0, sizeof(iter->init));
 	cpumask_clear(iter->started);
 	trace_seq_init(&iter->seq);
 	iter->pos = -1;
-- 
2.30.2